Non-ablative, optical phase-change data storage systems, record information in an optical phase-change memory material that is switchable between at least two detectable states by the application of optical energy. Optical phase-change memory material is typically incorporated in an optical recording medium having a structure such that the optical phase-change memory material is supported by a substrate and protected by encapsulants. In the case of optical recording media, the encapsulants include, for example, anti-ablation materials and layers, thermal insulation materials and layers, anti-reflection materials and layers, reflective layers, and chemical isolation layers. Moreover, various layers may perform more than one of these functions. For example, anti-reflection layers may also be anti-ablation layers and thermal insulating layers. The thicknesses of the layers, including the layer or layers of optical phase-change memory material, are engineered to minimize the energy necessary for effecting the state change as well as to optimize the high contrast ratio, high carrier-to-noise ratio and high stability of the optical phase-change memory materials.
Formation of optical recording media includes deposition of the individual layers by, for example, evaporative deposition, chemical vapor deposition, and/or plasma deposition. As used herein plasma deposition includes sputtering, glow discharge, and plasma assisted chemical vapor deposition.
An optical phase-change material is capable of being switched from one detectable state to another detectable state or states by the application of optical energy. The state of the phase-change changeable material is detectable by properties such as, for example, index of refraction, optical absorption, optical reflectivity, or combinations thereof. Tellurium based materials have been utilized as phase-change materials for data storage where the change is evidenced by a change in a physical property such as reflectivity. Tellurium based state changeable materials, in general, are single or multi-phased systems. The ordering phenomena of such materials includes a nucleation and growth process (including both or either homogeneous and heterogeneous nucleations) to convert a system of disordered materials to a system of ordered and disordered materials. The vitrification phenomena includes attaining a high mobility state and rapid quenching of the phase changeable material to transform a system of disordered and ordered materials to a system of largely disordered materials. The above phase changes and separations occur over relatively small distances, with intimate interlocking of the phases and gross structural discrimination, and may be highly sensitive to local variations in stoichiometry. The instant invention provides for high speed transformation by passing through a high mobility state. This high mobility state allows for high speed transformation from one state of relative order to another. The high mobility state does not specifically correspond to the molten state, but more accurately corresponds to a state of high system mobility.
Generally, a laser is used to supply the optical energy to cause the phase transitions between amorphous and crystalline states in an optical phase-change memory material. The amount of energy applied to the memory material is a function of both the power of the laser as well as the period of time that the laser pulse is applied. The crystallization energy is defined herein as the amout of energy per unit volume needed to substantially re-crystallize an amorphous region of the memory material. The crystallization energy is dependent upon many factors, including the energy necessary for nucleation during the crystallization process.
If the crystallization energy is too high, the memory material requires exposure to either a higher power laser pulse or a longer laser pulse in order to convert the material from the amorphous to the crystalline states. It is desireable to be able to control the crystallization energy of a phase-change memory material via the addition of one or more modifier elements. It is also desirable to increase the erasability of optical recording media.